A wrench is a tool for applying torque to fastener such as a nut, bolt, screw or the like for the purpose of tightening or slackening the fastener. The wrench has a head portion which is of a complementary shape to the periphery of the fastener in a non-rotatable manner so that a force applied to rotate the head transmits torque to the fastener. The fastener usually has an external polygonal shape, typically hexagonal or square, and the head of the wrench has a complementary internal shape and size. The head of a ring wrench is configured to substantially surround the periphery of the fastener.
The following description will refer particularly to wrenches for use with hexagonal nuts. However, it will be understood that the invention is equally applicable to wrenches and corresponding fasteners having other shapes.
A conventional ring wrench has a ring-shaped head having a curved, usually substantially circular external surface with a hexagonally shaped internal surface. Each internal surface of which can be substantially flat. In use the internal surface of the wrench head substantially engages the flat surfaces of the nut to put pressure on the corners when the fastener is tightened or slackened.
However, if the nut is undersized, damaged or worn, it is very likely that the head will “slip” and rotate around the nut burring the corners instead of properly gripping or engaging the flats or corners of the nut. A further embodiment of the present invention applies to a ratchet bar tool used for applying torque via an attached square drive and appropriate socket to a fastener for the purpose of tightening or slackening the fastener. The ratchet bar is movable relative to the socket in one direction only. Motion between the ratchet bar and the socket in the opposite direction is prevented by a set of angular teeth, which co-operate with a resilient pawl so as to create a locking motion in one direction only and free movement in the opposite direction. This operation of the socket and fastener via a ratchet bar is much more convenient in restrictive situations than the use of a fixed bar operated socket as there is seldom a requirement to remove and reattach the socket operating the fastener.
Variations of the ratchet bar are exhaustive. Most mechanisms have more and more locking teeth etc. to allow a smaller angle between drive, reposition and drive, resulting in mechanisms that whilst the angle between drive and reposition has been substantially reduced so has the amount of torque that can be safely applied to the ratchet bar without failure.